(1) The damage to the diode and transistor is generally due to PN junction breakdown or open circuit. Most of them are breakdown short circuits. In addition, there are two kinds of damage performance. One is the deterioration of thermal stability, which is normal when it is turned on and after a period of work. Another soft breakdown occurs because the characteristics of the PN junction are deteriorated. Measured with a multimeter Rx1K, each PN junction is normal, but it does not work properly after the machine is used. If you use RX10 or RX1 low range blocking, you will find that the NN junction is positive The resistance is larger than normal. You can use a pointer multimeter to measure the diode and triode on the road. The more accurate method is to set the multimeter to RX10 or Rx1 gear (usually use RX10 gear, and then use Rx1 gear when it is not obvious). Resistance. If the forward resistance is not too large (relative normal value), the reverse resistance is sufficiently large (relative to the positive value) to indicate that the PN junction is normal. Otherwise, it is doubtful. It needs to be welded and measured again. This is because the general electrical ranks second. 3. The external resistance of the non-polar tube is mostly above several hundred and several thousand ohms. With the low resistance of the multimeter, the resistance of the line side is blocked, and the influence of the external resistance on the PN junction resistance can be basically ignored.
(2) Damaged characteristics. The internal structure of the integrated circuit has many complex functions. Any part damaged can't work normally. There are also two types of damage to integrated circuits, including complete damage and poor thermal stability. When completely damaged. It can be removed. Comparing the normal and reverse resistance of each pin to the ground with the normal integrated circuit of the same model, you can always find one or a few pins with abnormal resistance. If the thermal stability is poor, you can use anhydrous alcohol to cool the suspected integrated circuit when the device is working. If the time of failure is delayed or no longer occurs, you can judge. Usually can only be eliminated by replacing the new integrated circuit.
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